T-Mobile sure hopes no one notices any difference with 5G VoNR

T-Mobile boasts that it now offers Voice over New Radio (VoNR), which is what enables it to offer voice services using 5G, in parts of two markets. It’s rolling it out, cautiously, across the country. But it really hopes no one notices the difference in their voice quality when going from 4G to 5G.

When it does reach markets beyond the pockets in Portland, Oregon, and Salt Lake City where it launched commercially on Friday, don’t expect much, according to Grant Castle, vice president of Device Engineering and Technology Labs at T-Mobile.

“It’s going to be super not exciting,” he said, noting there isn’t even anything visual for a customer to see. Sure, it’s an important stepping stone for T-Mobile, but it’s just one step on the bigger journey to provide a full 5G experience. “If we do this right, people will notice exactly no differences.”  

To be sure, voice over 5G has been in the works for a long time. T-Mobile President of Technology Neville Ray acknowledged as much during a UBS Future of 5G event on Friday, where he said “VoNR is tough” even for a company like T-Mobile with a lot of experience and a mature network.

He also alluded to the challenges that came with voice service over LTE, or VoLTE. Both 4G LTE and 5G launched first as data-only services. Voice was sort of added on later. That’s because voice is not very “data-app like,” Castle said. It prefers a consistent link and won’t tolerate the kinds of glitches that data permits.  

“It prefers a consistent link that is uninterrupted because voice needs to be flawless,” Castle said. “You can’t drop a packet here or there.” If you drop a packet during a movie streaming session, you’ll never notice it. But if it happens during a voice call, you’ll hear it.

“Voice is a surprisingly demanding application and it requires optimization on the phone,” the radio network, the core network and everything in between, Castle said.

Vendor mix

In T-Mobile’s press release, the company called out Ericsson, Nokia, Samsung and Qualcomm, representing infrastructure and handset/chipset partners and an indication of how many pieces need to come together. That’s part of why it takes so long. Initial interoperability was done with the chipset, and then additional testing was done with the chipset in the handset, as well as the infrastructure.

Portland is a Nokia market and Salt Lake City is an Ericsson market. T-Mobile uses a mix of these vendors across the country. “Our goal is to make sure it doesn’t matter,” Castle said. “It’s going to work on them both seamlessly.”

It doesn’t typically get a lot of ink, but he said that ensuring the devices work with government E-911 and location accuracy mandates is a very big deal. When a new voice layer is turned on, the operator is required to test directly with local PSAPs, the public safety answering points that handle emergency calls. The location and routing of these calls adds another layer of complexity to voice services.

T-Mobile boasts how it’s the first in the U.S. with a 5G standalone (SA) core, which is what’s required for a 5G VoNR voice service, but it’s not yet ready with network slicing, which is often cited as a big advantage for SA networks. For network slicing to work, it needs to be SA all the time, and until devices are available that are permanently connected to the SA network at all times, it won’t work as intended.

T-Mobile still has a fine LTE network, but all of its investment is going into 5G, he said. To wit: T-Mobile just shut down the old Sprint CDMA network. It doesn’t make sense to put LTE on that spectrum. So T-Mobile is going to aggregate the 1900 MHz spectrum and create another 5G channel. It will have its low-band 600 MHz, the 2.5 GHz and another layer that includes the 1900 MHz.

“You have to go to standalone to allow you to start to do carrier aggregation of three, four and multiple diverse channel bandwidths. That’s kind of where we’re going over the next year plus, getting people using multiple 5G bands simultaneously,” Castle said, referring to NR CA, or New Radio Carrier Aggregation.

Historically, T-Mobile in its early years as VoiceStream Wireless started out with the 1900 MHz spectrum, and that’s what it used for 2G and 3G. Then it used the AWS spectrum for LTE, and now that the older 2G and 3G technologies are getting retired, that 1900 MHz spectrum is leapfrogging up to 5G.

“Our goal is to be a pure 5G network for everyone,” he said. “That’s where we’re going.”